Gab Ibis

As urbanization and industrialization continue to shape the Philippines, a new environmental crisis has emerged, threatening the very ground beneath our feet.

Photo Courtesy of University of the Philippines.

A comprehensive study conducted by experts from the University of the Philippines has revealed alarming rates of ground subsidence across major metropolitan areas in the country, from Metro Manila to Legazpi City.

Led by Alfredo Mahar Francisco Lagmay, the team analyzed ground movement from 2014 to 2020 using an interferometric synthetic aperture radar, or InSAR, which found that some areas sink by as much as 109 millimeters per year.

In the Greater Manila Area, subsidence rates are highest in industrial zones, particularly in Bulacan, Cavite, and Laguna.

These areas, characterized by large factories and economic zones, require substantial water for their operations, leading to excessive groundwater extraction. As a result, the ground is slowly collapsing under the weight of urban development.

Residential areas are not immune to this phenomenon.        

Suburbs in Bulacan and Cavite, which have seen rapid population growth in recent years, are also sinking. The situation is worsened by the Marikina Valley Fault's proximity, which introduces additional risks of structural damage due to fault-related ground movement.

In these areas, residents have reported cracks in homes and infrastructure, a clear sign of the ongoing subsidence.

Outside urban centers, agricultural lands are also experiencing significant subsidence. In provinces like Bulacan, where rice fields and fishponds are prevalent, groundwater extraction for irrigation is causing the land to sink.

This not only threatens agricultural productivity but also increases the risk of flooding, particularly in coastal areas where sea levels are rising due to climate change.

In coastal towns like Obando, Bulacan, the impact of subsidence is already visible. Roads are submerged during high tides, and some homes are permanently flooded. Due to this, residents have resorted to elevating their houses or abandoning the ground floor altogether.

The worsening floods in these areas are not primarily due to increased rainfall but are instead a direct consequence of land subsidence, as the ground sinks faster than the sea level rises.

Currently, the National Water Resources Board regulates water extraction through permits, but the monitoring system is insufficient. With only 34 monitoring wells across the country, the scale of the problem far exceeds the current capacity for oversight.

InSAR technology offers a promising solution for long-term monitoring of ground subsidence.

By analyzing a series of interferograms over time, authorities can identify areas at risk and take preventive measures.

However, this requires investment in technology and infrastructure, as well as stricter enforcement of groundwater extraction regulations.

Without intervention, the subsidence will continue to worsen, posing a significant threat to the environment, infrastructure, and the livelihoods of millions of Filipinos.

The sinking cities of the Philippines are a stark reminder of the need for sustainable development practices and the urgent need to address environmental issues before they reach a tipping point – and destroy the very ground beneath our feet.